Unmanaged
Solutions can be exported as either managed or unmanaged. Managed are read only versions, so when imported they can not be edit.
Unmanaged allows you to convert managed solutions to unmanaged when the developer version has been lost.

Simply drag the managed solution onto the drag and drop rectangle or click to upload and select the export.
The unmanaged version will then be automatically downloaded to your download file.
How It Works
Solutions contain mulitple files, including a solution.xml file. This file has a <managed> tag, when set to 0 it is unmanaged, 1 is managed. Unmanaged simply changes it from 1 to 0. You can do it yourself without unmanaged by:
Copy solution.xml our of zip
Edit and Save the file
Copy back into the zip file
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